A steering angle sensor for determining the steering wheel angle can include a code track assigned to a rotatable portion of the steering wheel arrangement or a fixed portion of thereof. For example, a rotor with the track can rotate together with the steering wheel, and a sensor for sensing the code track can be assigned to a fixed stator. When the sensor senses the track, it generates a signal from which the current steering angle can be determined. See for example, German patent publication DE 197 58 104 A1. Such a steering angle sensor determines the absolute value of the angle of rotation.
Alternatively, the code track may be embodied as an incremental track and an incremental signal, i.e., a signal that only identifies the change in the steering angle from the previous signal, but not the absolute value of the steering angle.
To control certain functional groups of a motor vehicle, for example the brake system, as a function of the steering angle, it is not only desirable to sense the change in the steering angle but also the absolute value of the steering angle. In this regard, it is known to arrange the steering angle sensor along an incremental track and an additional track that contains at least one reference mark, which can be used to generate a signal from which the value of the steering angle can be directly derived. The respective current steering angle can be determined with a high degree of accuracy from the combination of this reference signal with the incremental signal, which has a very high angular resolution. Such a steering angle sensor, however, is disadvantageous because it requires a more complicated design and is more expensive to manufacture than steering angle sensors based on a pure incremental measuring system. Moreover, it takes up more space.
Accordingly, there is a need for an improved, more-cost effective steering angle sensor for determining both the absolute and incremental values of the steering angle, without taking up additional space. The present invention addresses this need.
The present invention relates to a steering angle sensor, system, method, and incremental track thereof for determining the steering angle of a steering wheel.
One aspect of the present invention is the incremental track, which includes at least one reference mark for modifying an incremental signal generated by sensing the incremental track.
The track can include a plurality of spaced incremental marks arranged along a predetermined path, which can be annular. The incremental marks are configured, when sensed, to generate an incremental signal containing rise edge and a fall edge indicative of the demarcation of the incremental marks. The reference mark can be positioned or arranged between the incremental markings on the incremental track. For instance, the reference mark can be formed between an adjacent pair of the incremental markings or spacings between the incremental markings to hide the rise and fall edges of the incremental markings.
The incremental markings can be spaced apart evenly, i.e., periodically, from each other along the predetermined path or the direction in which the incremental track extends. The incremental markings can comprise a periodic bar structure, The reference mark can be identical to the incremental markings. The reference mark can be contiguous with one of the incremental markings to form a marking area having twice the width of the incremental marking. Alternatively, the reference mark can be formed between and contiguous with a pair of adjacent incremental markings to form a marking area having three times the width of the incremental marking.
The reference mark can have a same length as the incremental marks so that the reference mark extends no further than the incremental marks along a direction transverse to a direction in which the incremental track extends.
The incremental track can include alternating incremental markings, with an intermediate spacing between any adjacent pairs of the incremental markings, except where the reference mark is formed. The reference mark can be formed at at least one of the spacings or at least one of the markings.
The reference mark can be formed by converting at least one incremental marking or at least one intermediate spacing to the other. The reference mark also can be formed by replacing at least one intermediate space with the incremental marking or by replacing at least one incremental marking with an intermediate space. It can also be formed by changing the shape, extent, or structure of the incremental marking or the intermediate spacing.
Another aspect of the invention is the steering angle sensor, which can include any aspect of the incremental track described above, and a sensing device. The incremental track is configured to be associated with one of a rotatable portion and a fixed portion of a steering wheel arrangement. The steering wheel is rotatable along with the rotatable portion relative to the fixed portion.
The sensing device is for sensing the incremental track and generating incremental signals for determining the steering angle. The sensing device is configured to be associated with the other of the rotatable and fixed portions. The sensing device comprises at least two sensor elements spaced along the incremental track along the direction in which the incremental track extends. More specifically, the sensing device comprises three sensor elements serially arranged and spaced at equal distances. The sensor elements are spaced apart at a distance that is unequal to the spacing of the incremental markings.
Another aspect of the present invention is the steering angle determining system for a motor vehicle. This system can include the steering angle sensor described above having at least first and second sensor elements for generating first and second incremental signals, and an evaluator for determining the respective current steering angle based on the first and second incremental signals. The evaluator calculates the change in the steering angle based on the first and second incremental signals, and compensates the first incremental signal if the second incremental signal determines that the first incremental signal lacks an incremental signal component resulting from detecting the reference mark, which modifies the incremental signal. The evaluator determines the hidden edges based on the first and second incremental signals and compensates therefor in determining the steering angle.
Another aspect of the present invention is the method of determining the steering angle of a steering wheel in a motor vehicle. This method can involve the steps of providing the incremental track, which can be associated with one of a rotatable portion and a fixed portion of a steering wheel arrangement, providing the sensing device having at least the first and second sensor elements respectively for generating first and second incremental signals, providing at least one reference mark in the incremental track for modifying the first and second incremental signals, detecting the first and second incremental signals from the first and second sensor elements, and determining the respective current steering angle based on the first and second incremental signals. The change in the steering angle can be determined by evaluating the first and second incremental signals and compensating the first incremental signal if the second incremental signal determines that the first incremental signal lacks an incremental signal component resulting from detecting the reference mark, which modifies the incremental signal.